The radius of each wheel of a car is 16 inches. At how many revolutions per minute should a spin balancer be set to balance the tires at a speed of 90 miles per hour? What is the setting for a wheel of radius 14 inches?

base figures you need to know
5280 feet in a mile
12 inches in a foot
60 minutes in an hour
The circumference of a circle formula is circumference = pi * radius * 2

the trick of this problem is you have feet in the mile but inches in the tire & hours in the speed but minutes in the revolutions

so you would have your speed (90) miles per hour divided by (60) minutes times the number of feet in a mile (5280) times number of inches in a foot (12) divided by the circumference of the tire pi * r2 (3.141593 * 16 * 2)